1. Technical Field
The present invention relates to a semiconductor device in which upper and lower wiring layers are connected through a contact hole and a method for manufacturing the semiconductor device. In particular, this invention relates to a semiconductor device that can improve wiring reliability at a contact hole and a method for manufacturing the semiconductor device.
2. Related Art
FIGS. 4A, 4B and 4C are sectional views for explaining an example of related art for a method for manufacturing a semiconductor device. The semiconductor device manufactured by this example has upper and lower wiring layers that are connected by a tungsten plug.
First, as shown in FIG. 4A, a first wiring layer 120 is formed on an insulating film 110. The first wiring layer 120 has a structure in which a barrier film 121, an Al alloy film 122 and an antireflection film 123 are deposited in this order. The antireflection film 123 has a structure in which a Ti film and a TiN film are deposited in this order. Subsequently, an interlayer insulating film 130 that is mainly made of silicon oxide is formed on the insulating film 110 and the first wiring layer 120. Then, after a surface of the interlayer insulating film 130 is planarized, a contact hole 130a is formed in the interlayer insulating film 130 to be on the first wiring layer 120.
After the above process, a residue from etching remains on a surface of the antireflection film 123 at the bottom of the contact hole 130a. Further, an oxide layer is formed on the surface of the antireflection film 123 because of an air exposure. Therefore, the first wiring layer 120 that is exposed at the bottom of the contact hole 130a is sputtered with Ar plasma. Thus the residue remaining on the surface of the antireflection film 123 and the oxide layer are removed. The removed residue and oxide layer attach to the sidewall of the contact hole 130a as an island-like oxide 131.
Subsequently, a barrier film 141 made of TiN is formed on the interlayer insulating film 130, and also on the sidewall and the bottom surface of the contact hole 130a. Due to the attachment of the island-like oxide 131 to the sidewall of the contact hole 130a, coverage of the barrier film 141 around the oxide 131 may decrease.
Next, as shown in FIG. 4B, a tungsten film 142 is formed on the barrier film 141 and in the contact hole 130a by chemical vapor deposition (CVD). As a raw material gas, Tungsten Hexafluoride (WF6) is used. In a case where coverage of the barrier film 141 on the sidewall of the contact hole 130a is insufficient and the interlayer insulating film 130 is partially exposed, the tungsten film 142 comes in contact with the interlayer insulating film 130 directly at this exposed section 130b. However, because adhesion of these two films is insufficient, an air gap 130c is made between the tungsten film 142 and the interlayer insulating film 130 on the exposed section 130b. 
Then, as shown in FIG. 4C, the tungsten film 142 and the barrier film 141 on the interlayer insulating film 130 are removed, which completes a tungsten plug 140 deposited in the contact hole 130a. Subsequently, a second wiring layer 150 is formed on the interlayer insulating film 130 to be on the tungsten plug 140. The second wiring layer 150 has a structure in which a barrier film 151, an AlCu alloy film 152 and an antireflection film 153 are deposited in this order (as referred to the second paragraph of JP-A-9-283624 as an example of related art).
As mentioned above, when an island-like oxide adheres to a sidewall of a contact hole, a partial gap may be made between the sidewall of the contact hole and an electrical conductor in a process to deposit the electrical conductor (a tungsten plug for example) into the contact hole. In this case, connection reliability (stress migration characteristics or electromigration characteristics for example) at the contact hole decreases.
As another case where an island-like oxide adheres to a sidewall of a contact hole, a barrier film may be detached from the sidewall of the contact hole and thus wiring reliability (stress migration characteristics or electromigration characteristics for example) at the contact hole may decrease.